Non-linearity cancellation in a dual-path ADC

ABSTRACT

The overall performance of a dual-path ADC system may be improved by using a VCO-based ADC for small-amplitude signals and employing non-linear cancellation to remove nonlinearities in signals output by the VCO-based ADC. In particular, VCO-based dual-path ADC systems of this disclosure may be configured to receive a first digital signal from a first ADC and a second digital signal from a second ADC, wherein the second digital signal is more non-linear than the first digital signal. The dual-path systems may also be configured to determine one or more non-linear coefficients of the second digital signal based, at least in part, on processing of the first and second digital signals. The dual-path systems may be further configured to modify the second digital signal based, at least in part, on the determined one or more non-linear coefficients to generate a more linear second digital signal.

FIELD OF THE DISCLOSURE

The instant disclosure relates to analog-to-digital converters (ADCs).More specifically, portions of this disclosure relate to non-linearitycancellation of an open-loop voltage-controlled oscillator (VCO) basedADC in a dual-path ADC.

BACKGROUND

Dual-path ADCs are used to apply different transfer functions todifferent types of signals. For example, FIG. 1 provides an exampleschematic block diagram illustrating a conventional dual-path ADC systemaccording to the prior art. A conventional dual-path ADC system 100 hasa first channel (path) 110 that includes a high dynamic range ADC 112,such as an ADC having a dynamic range of 100 dB, preceded by ananti-aliasing filter (AAF) 114 but no gain element. System 100 alsoincludes a second channel 120 that includes a high dynamic range ADC 122preceded by an AAF 124 having a programmable gain element. The firstchannel 110 and the second channel 120 receive input from an input node130.

In dual-path ADC system 100, first channel 110 can be used to processsignals with high amplitudes and second channel 120 can be used toprocess signals with low amplitudes. For example, if a strong signal isreceived at the input 130, then the output of channel 120 is a clippedversion of the input signal while the output of channel 110 is a linearversion of the input signal having a high dynamic range because theamplitude of the input signal is inherently high. In such a scenario,the output of channel 110 may be used as the digital representation ofthe input signal that gets post-processed. However, if a weak signal isreceived at the input 130, then the output of neither channel 110 or 120is clipped, but the output of channel 120 will have a higher dynamicrange because of the amplification applied by amplification block 124.In such a scenario, the output of channel 120 may be used as the digitalrepresentation of the input signal that gets post-processed.

Numerous drawbacks are associated with conventional dual-path ADCsystems, such as system 100. For example, in order to achieve highdynamic range via the weak signal path 120, the amplifier 124 isrequired. However, the amplifier tends to cause more noise and requirethe overall system to consume more power and area.

Shortcomings mentioned here are only representative and are includedsimply to highlight that a need exists for improved electricalcomponents, particularly for improved ADCs. Embodiments described hereinaddress certain shortcomings but not necessarily each and every onedescribed here or known in the art.

SUMMARY

The overall performance of a dual-path ADC system may be improved byusing a VCO-based ADC for small-amplitude signals and employingnon-linear cancellation to remove nonlinearities in signals output bythe VCO-based ADC. An ADC system with two paths may be used to implementthis processing technique. According to one embodiment, a dual-path ADCsystem may include a first analog to digital converter (ADC) configuredto receive an input signal from an input terminal and generate a firstdigital signal; a second ADC configured to receive the input signal fromthe input terminal and generate a second digital signal, wherein thesecond digital signal is more non-linear than the first digital signal;and a digital signal processing block configured to: receive the firstdigital signal and the second digital signal; determine one or morenon-linear coefficients of the second digital signal based, at least inpart, on processing of the first and second digital signal; and/ormodify the second digital signal based, at least in part, on thedetermined one or more non-linear coefficients to generate a more linearsecond digital signal. In some embodiments, the first ADC comprises aclosed-loop ADC and the second ADC comprises an open-loop voltagecontrolled oscillator-based (VCO-based) ADC. According to anotherembodiment, the second ADC is configured to amplify the received inputsignal. In another embodiment, the first ADC is further configured toreceive input signals having an amplitude higher than input signals forwhich the second ADC is configured to receive.

In certain embodiments, the digital signal processing block isconfigured to: generate one or more non-linear components of the seconddigital signal based, at least in part, on the determined one or morenon-linear coefficients; and/or subtract the generated one or morenon-linear components from the second digital signal. According toanother embodiment, the digital signal processing block may also beconfigured to: filter the first and second digital signal; and/or selectone of the filtered first digital signal and the filtered second digitalsignal for further processing. In some embodiments, to perform theselecting, the digital signal processing block may be configured to:select the filtered first digital signal when a signal strengthassociated with the input signal is equal to or exceeds a thresholdsignal strength; and/or select the filtered second digital signal whenthe signal strength associated with input signal is less than thethreshold signal strength.

According to another embodiment, a method includes receiving a firstdigital signal from a first analog to digital converter (ADC); receivinga second digital signal from a second ADC, wherein the second digitalsignal is more non-linear than the first digital signal; determining oneor more non-linear coefficients of the second digital signal based, atleast in part, on processing of the first and second digital signal;and/or modifying the second digital signal based, at least in part, onthe determined one or more non-linear coefficients to generate a morelinear second digital signal.

In certain embodiments, the step of modifying comprises: generating oneor more non-linear components of the second digital signal based, atleast in part, on the determined one or more non-linear coefficients;and subtracting the generated one or more non-linear components from thesecond digital signal.

In some embodiments, the method further includes: filtering the firstand second digital signal; and/or selecting one of the filtered firstdigital signal and the filtered second digital signal for furtherprocessing. According to an embodiment, the step of selecting comprises:selecting the filtered first digital signal when a signal strengthassociated with an input signal used to generate the first digitalsignal is equal to or exceeds a threshold signal strength; and/orselecting the filtered second digital signal when the signal strengthassociated with the input signal used to generate the second digitalsignal is less than the threshold signal strength.

According to another embodiment, a mobile device may include acontroller integrated circuit (IC) configured to perform the stepscomprising: receive a first digital signal from a first analog todigital converter (ADC); receive a second digital signal from a secondADC, wherein the second digital signal is more non-linear than the firstdigital signal; determine one or more non-linear coefficients of thesecond digital signal based, at least in part, on processing of thefirst and second digital signal; and/or modify the second digital signalbased, at least in part, on the determined one or more non-linearcoefficients to generate a more linear second digital signal. In someembodiments, the first ADC comprises a closed-loop ADC and the secondADC comprises an open-loop VCO-based ADC. In another embodiment, thecontroller comprises an audio coder/decoder (CODEC).

In certain embodiments, modifying comprises the controller being furtherconfigured to perform the steps comprising: generating one or morenon-linear components of the second digital signal based, at least inpart, on the determined one or more non-linear coefficients; and/orsubtracting the generated one or more non-linear components from thesecond digital signal.

In some embodiments, the controller is further configured to perform thesteps comprising: filtering the first and second digital signal; and/orselecting one of the filtered first digital signal and the filteredsecond digital signal for further processing. According to anembodiment, selecting, by the controller, comprises the controller beingfurther configured to perform steps comprising: selecting the filteredfirst digital signal when a signal strength associated with an inputsignal used to generate the first digital signal is equal to or exceedsa threshold signal strength; and/or selecting the filtered seconddigital signal when the signal strength associated with the input signalused to generate the second digital signal is less than the thresholdsignal strength.

The foregoing has outlined rather broadly certain features and technicaladvantages of embodiments of the present invention in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter that form thesubject of the claims of the invention. It should be appreciated bythose having ordinary skill in the art that the conception and specificembodiment disclosed may be readily utilized as a basis for modifying ordesigning other structures for carrying out the same or similarpurposes. It should also be realized by those having ordinary skill inthe art that such equivalent constructions do not depart from the spiritand scope of the invention as set forth in the appended claims.Additional features will be better understood from the followingdescription when considered in connection with the accompanying figures.It is to be expressly understood, however, that each of the figures isprovided for the purpose of illustration and description only and is notintended to limit the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed systems and methods,reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings. In the appended figures, similarcomponents or features may have the same reference label. Further,various components of the same type may be distinguished by followingthe reference label with a second label that distinguishes among thesimilar components. If just the first reference label is used in thespecification, the description is applicable to any one of the similarcomponents having the same first reference label irrespective of thesecond reference label.

FIG. 1 is an example schematic block diagram illustrating a conventionaldual-path ADC system according to the prior art.

FIG. 2 is an example schematic block diagram illustrating a VCO-baseddual-path ADC system with non-linear cancellation of a VCO-based ADC inthe dual-path ADC system according to one embodiment of the disclosure.

FIG. 3A is an example schematic block diagram illustrating details of aVCO-based ADC in a dual-path ADC system according to one embodiment ofthe disclosure.

FIG. 3B is a linearized system-level diagram of the open-loop VCO-basedADC illustrated in FIG. 3A according to one embodiment of thedisclosure.

FIG. 4 is an example schematic block diagram illustrating non-linearcancellation for a dual-path ADC system according to one embodiment ofthe disclosure.

FIG. 5 is an example schematic block diagram illustrating non-linearcancellation performed in a VCO-based dual-path ADC system withnon-linear cancellation according to one embodiment of the disclosure.

FIG. 6 is an example flow chart illustrating a method for non-linearitycancellation of an open-loop VCO-based ADC in a dual-path ADC accordingto one embodiment of the disclosure.

DETAILED DESCRIPTION

FIG. 2 is an example schematic block diagram illustrating a VCO-baseddual-path ADC system 200 with non-linear cancellation of a VCO-based ADCin the dual-path ADC system 200 according to one embodiment of thedisclosure. In some embodiments, system 200 may be implemented as (orwithin) a controller integrated circuit (IC), such as an audiocoder/decoder (CODEC). The VCO-based dual-path ADC system 200 includes afirst ADC path 210. First ADC path 210 includes a first ADC 220configured to receive an input signal from an input node 260 and alsoconfigured to generate a first digital signal Y1. In some embodiments,first ADC 220 may be a closed-loop ADC. According to one embodiment,first ADC 220 may be implemented as a closed-loop ADC using aswitched-capacitor-based modulator. In another embodiment, first ADC 220may be implemented as a closed-loop ADC using a continuous-time-basedmodulator. First ADC 220 may be configured to have a high dynamic range,such as a dynamic range of at least 100 dBFS (decibels relative to fullscale). First ADC 220 may also be configured to handle strong inputsignals, such as signals having amplitudes of near 0 dBFS, or weaksignals as small as 60 dBFS.

The VCO-based dual-path ADC system 200 also includes a second ADC path230. Second ADC path 230 includes a second ADC 240 configured to receivethe input signal from the input node 260 and generate a second digitalsignal. According to an embodiment, second ADC 240 may be an open-loopVCO-based ADC. In some embodiments, second ADC 240 may be configured tohave a high dynamic range, such as a dynamic range of at least 100 dB.According to an embodiment, the high dynamic range of the VCO-based ADC240 may be achieved with the internal gain of the VCO-based ADC 240. Inother words, the high dynamic range of the VCO-based ADC 240 may beachieved without the use of pre-amplifiers, such as amplifier 124 usedin channel 120 of prior art system 100, to increase the dynamic range ofADC channel 124 in prior art system 100.

FIG. 3A provides an example schematic block diagram illustrating detailsof a VCO-based ADC in a dual-path ADC system according to one embodimentof the disclosure; and FIG. 3B provides a linearized system-leveldiagram of the open-loop VCO-based ADC illustrated in FIG. 3A accordingto one embodiment of the disclosure. VCO-based ADC 340 may be onedifferential-input implementation of single-ended VCO-based ADC 240illustrated in FIG. 2, in which high dynamic range may be achieved withthe internal gain of the VCO-based ADC 340. As illustrated in FIG. 3A,VCO-based ADC 340 may include an internal transconductance block 342,current-controlled oscillators (CCOs) 344A and 344B, counters 346A and346B, a subtractor block 348, and a differentiator block 349.Transconductance block 342 may convert the input voltage signals 360Aand 360B to current signals. The current signals output bytransconductance block 342 may be transferred to CCOs 344 to control theoperation of CCOs 344 as a function of the current signals. Counters 346(e.g., counters 346A and 346B) may be configured to operate at asampling rate, such as T_(clk), and sample the outputs of CCOs 344 toconvert the analog signals received from CCOs 344 to digital signals.The digital signals output by counters 346 may be subtracted from eachother at subtractor block 348 to obtain the digital representation forthe input voltage signals 360. In some embodiments, counters 346 andsubtractor block 348 may perform operations similar to a quantizationblock. Differentiator block 349 may be configured to receive the signaloutput from subtractor block 348 and output a differentiated digitalsignal representation for the input voltage signals 360. The output ofdifferentiator block 349 may be post-processed as a digitalrepresentation of the input voltage signals 360.

Transconductance block 342 and CCOs 344 may be configured to provideamplification of input signals VIP and VIN receive at input nodes360A-B. For example, in converting the input voltage signals 360 tocurrents, transconductance block 342 may be configured to provide afirst amount of amplification. In addition, CCOs 344 may be configuredto implement a second amount of amplification. For example, CCOs 344 maybe configured to modify their operation in response to the currentsupplied by transconductance block 342 in such a manner that the outputcorresponds to an amplification of the input current signals provided bytransconductance block 342.

In some embodiments, the amplification provided by transconductanceblock 342 and CCOs 344 may provide higher amplification than can beachieved with using pre-amplifiers preceding an ADC, such aspre-amplifier 124 used in channel 120 of prior art system 100 toincrease the dynamic range of ADC channel 124 in prior art system 100.Accordingly, in response to a weak input signal, higher dynamic rangemay be achieved with VCO-based ADC 340 than can be achieved by prior artsystems. In addition, in dual-path VCO-based ADCs of this disclosure,the VCO-based ADC of a dual-path ADC, such as second ADC 240 or ADC 340,may be configured to handle weak input signals while still providinghigh dynamic range outputs similar to the high dynamic range outputsprovided by closed-loop ADCs implemented in dual-path ADCs of thisdisclosure, such as closed-loop ADC 220.

In addition to providing amplification, a dual-path ADC utilizing aVCO-based ADC, such as VCO-based ADC 240 or 340, may yield higheroverall metrics than a conventional dual-path ADC with pre-amplifiers.For example, because internal features of VCO-based ADCs may be used toprovide amplification, pre-amplifiers needed to process weak inputsignals are not needed for dual-path ADCs utilizing VCO-based ADCs. Byremoving the pre-amplifiers, dual-path VCO-based ADC systems of thisdisclosure may remove the extra noise contributions from thepre-amplifiers, such as the resistors used in the pre-amplifiers.Accordingly, in a dual-path VCO-based ADC system, such as systems 200 or300, the majority of the thermal noise budget for the system may beallocated to transconductance block 340. In addition, by removing thepre-amplifiers, and other circuitry needed to operate with thepre-amplifiers, dual-path VCO-based ADC systems of this disclosure maybe configured to have less area and consume less power, this in additionto having less noise contributors early in the signal path.

In some embodiments, the digital signal output by VCO-based ADC 340 maybe more non-linear than the digital signal output by ADC 220 because aVCO-based ADC is inherently more non-linear due to its open-loop design.By contrast, closed-loop ADCs, such as ADC 220, may have theirnon-linearity improved by the closed-loop mechanisms of the system.Accordingly, in some embodiments, the second digital signal output bythe second ADC path that includes VCO-based ADC 240 may be morenon-linear than the first digital signal output by the first ADC paththat includes closed-loop ADC 220.

Returning to FIG. 2, VCO-based dual-path ADC system 200 also includes adigital signal processing block 250. Digital signal processing block 250may be configured to process signals received from the dual paths. Insome embodiments, the digital signal processing block 250 may employdigital calibration techniques to reduce the amount of non-linearitypresent in signals propagating through second ADC path 230 that includesVCO-based ADC 240. Digital signal processing block 250 may also beconfigured to filter signals received via first ADC path 210 and/orsecond ADC path 230. According to an embodiment, digital signalprocessing block 250 may also be configured to select one of either thefirst digital signal output by the first ADC path 210 or the seconddigital signal output by the second ADC path 230 for additionalprocessing.

Digital signal processing block 250 may include decimation filters 252Aand 252B, attenuator 254, and control unit 256. Decimation filters 252Aand 252B may be configured to filter the signals received from first ADCpath 210 and/or second ADC path 230. For example, decimation filter 252Amay be used to filter the first digital signal output by ADC path 210and decimation filter 252B may be used to filter the second digitalsignal output by ADC path 230. Attenuator 254 may be used to attenuatethe filtered second digital signal output by ADC path 230.

Control unit 256 may be configured to select one of the filtered firstdigital signal and the filtered second digital signal for furtherprocessing. For example, control unit 256 may be configured to selectthe filtered first digital signal output by ADC path 210 when a signalstrength associated with the input signal V_(IN) from input node 260 isequal to or exceeds a threshold signal strength. By contrast, controlunit 256 may be configured to select the filtered second digital signaloutput by ADC path 230 when the signal strength associated with theinput signal V_(IN) is less than the threshold signal strength. In someembodiments, control unit 256 may also be configured to perform digitalcalibration to reduce the amount of non-linearity present in the signalwhen the selected signal is the filtered second digital signal output bythe second ADC path 230.

FIG. 4 provides an example schematic block diagram illustratingnon-linear cancellation for a dual-path ADC system according to oneembodiment of the disclosure. The non-linear cancellation illustrated inFIG. 4 may be the non-linear cancellation performed in control unit 256of digital signal processing block 250. As illustrated in FIG. 4,control unit 256 may include a digital unit 430 configured to receive afirst digital signal 410 and a second digital signal 420. As illustratedin FIG. 2, the first digital signal 410 may be the filtered version ofthe first digital signal output by the first ADC path 210 and the seconddigital signal 420 may be the filtered and attenuated version of thesecond digital signal output by the second ADC path 230. In otherembodiments, first digital signal 410 and second digital signal 420 maybe the unfiltered and/or unattenuated versions of the digital signalsoutput by the first ADC path 210 and the second ADC path 230.

Digital unit 430 may be configured to determine one or more non-linearcoefficients of the second digital signal based, at least in part, onprocessing of the first and second digital signal. For example, asillustrated in the embodiment of FIG. 2, the first digital signal may bea linear signal 272 and the second digital signal may be a third-ordernon-linear signal 270. Thus, the first digital signal and the seconddigital signal may be respectively represented as:V _(o1) =A sin(ωt)V ₀₂ =A sin(ωt)+α₃(A sin(ωt))³.Using cross-correlation, the third-order non-linearity coefficient maybe determined as:

${C\; C} = {{V_{01} \otimes V_{02}} = {\left. {\frac{A^{2}}{2}\left( {1 + {\frac{3\alpha_{3}}{4}A^{2}}} \right)}\rightarrow\alpha_{3} \right. = {\frac{4}{3\; A^{2}}{\left( {\frac{{2 \cdot C}\; C}{A^{3}} - 1} \right).}}}}$With the one or more non-linear coefficients of the second digitalsignal determined, the digital unit 430 may be configured to modify thesecond digital signal based, at least in part, on the determined one ormore non-linear coefficients to generate a more linear second digitalsignal. For example, digital unit 430 may be configured to generate oneor more non-linear components of the second digital signal based, atleast in part, on the determined one or more non-linear coefficients andsubtract the generated one or more non-linear components from the seconddigital signal. In particular, FIG. 4 illustrates that after thethird-order non-linearity coefficient 450 has been determined, thethird-order non-linearity component can be generated by cubing the firstdigital signal 410 using cubing block 440 and then multiplying the cubedresult by the determined third-order non-linear coefficient. Thegenerated third-order non-linear component 460 may then be subtractedfrom the second digital signal 420 to produce a modified second digitalsignal 580, output as signal D_(OUT) of FIG. 5, in which the third-ordernon-linearity component has been removed. In some embodiments, after thenon-linear coefficients for the VCO-based ADC 240 have been determinedduring the calibration phase disclosed above with reference to FIG. 4,the non-linear coefficients may be used during normal operation of theVCO-based dual-path ADC system 200 to remove non-linearity of signalspropagating through second ADC path 230.

Although the operations for removing third-order non-linearitycomponents have been described in detail herein, one of skill in the artwould readily recognize that the same operations may be used to performcancellation of higher-order non-linear components. For example, thesame operations may be used to cancel fifth-order non-linear componentsof digital signals output by second ADC path 230 that includes VCO-basedADC 240.

FIG. 6 is an example flow chart illustrating a method for non-linearitycancellation of an open-loop VCO-based ADC in a dual-path ADC accordingto one embodiment of the disclosure. Method 600 may be implemented withthe systems described with respect to FIGS. 2-5 or other systems. Method600 begins, at block 602, with receiving a first digital signal from afirst analog to digital converter (ADC). At block 604, the method 600includes receiving a second digital signal from a second ADC, whereinthe second digital signal is more non-linear than the first digitalsignal. At block 606, method 600 includes determining one or morenon-linear coefficients of the second digital signal based, at least inpart, on processing of the first and second digital signal.

At block 608, method 600 includes modifying the second digital signalbased, at least in part, on the determined one or more non-linearcoefficients to generate a more linear second digital signal. In someembodiments, the modifying step of block 608 may include generating oneor more non-linear components of the second digital signal based, atleast in part, on the determined one or more non-linear coefficients andsubtracting the generated one or more non-linear components from thesecond digital signal.

In some embodiments, the systems described with respect to FIGS. 2-5 mayalso perform the steps of filtering the first and second digital signaland selecting one of the filtered first digital signal and the filteredsecond digital signal for further processing. According to anembodiment, selecting may include selecting the filtered first digitalsignal when a signal strength associated with an input signal used togenerate the first digital signal is equal to or exceeds a thresholdsignal strength and selecting the filtered second digital signal whenthe signal strength associated with the input signal used to generatethe second digital signal is less than the threshold signal strength.

The schematic flow chart diagram of FIG. 6 is generally set forth as alogical flow chart diagram. As such, the depicted order and labeledsteps are indicative of aspects of the disclosed method. Other steps andmethods may be conceived that are equivalent in function, logic, oreffect to one or more steps, or portions thereof, of the illustratedmethod. Additionally, the format and symbols employed are provided toexplain the logical steps of the method and are understood not to limitthe scope of the method. Although various arrow types and line types maybe employed in the flow chart diagram, they are understood not to limitthe scope of the corresponding method. Indeed, some arrows or otherconnectors may be used to indicate only the logical flow of the method.For instance, an arrow may indicate a waiting or monitoring period ofunspecified duration between enumerated steps of the depicted method.Additionally, the order in which a particular method occurs may or maynot strictly adhere to the order of the corresponding steps shown.

If implemented in firmware and/or software, functions described abovemay be stored as one or more instructions or code on a computer-readablemedium. Examples include non-transitory computer-readable media encodedwith a data structure and computer-readable media encoded with acomputer program. Computer-readable media includes physical computerstorage media. A storage medium may be any available medium that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise random access memory (RAM),read-only memory (ROM), electrically-erasable programmable read-onlymemory (EEPROM), compact disc read-only memory (CD-ROM) or other opticaldisk storage, magnetic disk storage or other magnetic storage devices,or any other medium that can be used to store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Disk and disc includes compact discs (CD), laser discs,optical discs, digital versatile discs (DVD), floppy disks and Blu-raydiscs. Generally, disks reproduce data magnetically, and discs reproducedata optically. Combinations of the above should also be included withinthe scope of computer-readable media.

In addition to storage on computer readable medium, instructions and/ordata may be provided as signals on transmission media included in acommunication apparatus. For example, a communication apparatus mayinclude a transceiver having signals indicative of instructions anddata. The instructions and data are configured to cause one or moreprocessors to implement the functions outlined in the claims.

Although the present disclosure and certain representative advantageshave been described in detail, it should be understood that variouschanges, substitutions and alterations can be made herein withoutdeparting from the spirit and scope of the disclosure as defined by theappended claims. Moreover, the scope of the present application is notintended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. For example, although analog-to-digitalconverters (ADCs) are described in embodiments above, aspects of thedisclosed invention may also be applied to digital-to-analog converters(DACs) or digital-to-digital converters. As one of ordinary skill in theart will readily appreciate from the present disclosure, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

What is claimed is:
 1. An apparatus, comprising: a first analog todigital converter (ADC) configured to receive an input signal from aninput terminal and generate a first digital signal; a second ADCconfigured to receive the input signal from the input terminal andgenerate a second digital signal, wherein the second digital signal ismore non-linear than the first digital signal; and a digital signalprocessing block configured to: receive the first digital signal and thesecond digital signal; determine one or more non-linear coefficients ofthe second digital signal based, at least in part, on processing of thefirst and second digital signals; and modify the second digital signalbased, at least in part, on the determined one or more non-linearcoefficients to generate a more linear second digital signal.
 2. Theapparatus of claim 1, wherein the digital signal processing block isconfigured to: generate one or more non-linear components of the seconddigital signal based, at least in part, on the determined one or morenon-linear coefficients; and subtract the generated one or morenon-linear components from the second digital signal.
 3. The apparatusof claim 1, wherein the first ADC comprises a closed-loop ADC.
 4. Theapparatus of claim 1, wherein the second ADC comprises an open-loopvoltage controlled oscillator-based (VCO-based) ADC.
 5. The apparatus ofclaim 1, wherein the second ADC is configured to amplify the receivedinput signal.
 6. The apparatus of claim 1, wherein the digital signalprocessing block is further configured to: filter the first and seconddigital signals; and select one of the filtered first digital signal andthe filtered second digital signal for further processing.
 7. Theapparatus of claim 6, wherein the digital signal processing block beingconfigured to: select the filtered first digital signal when a signalstrength associated with the input signal is equal to or exceeds athreshold signal strength; and select the filtered second digital signalwhen the signal strength associated with input signal is less than thethreshold signal strength.
 8. The apparatus of claim 1, wherein thefirst ADC is further configured to receive input signals having anamplitude higher than input signals for which the second ADC isconfigured to receive.
 9. A method, comprising: receiving a firstdigital signal from a first analog to digital converter (ADC); receivinga second digital signal from a second ADC, wherein the second digitalsignal is more non-linear than the first digital signal; determining oneor more non-linear coefficients of the second digital signal based, atleast in part, on processing of the first and second digital signals;and modifying the second digital signal based, at least in part, on thedetermined one or more non-linear coefficients to generate a more linearsecond digital signal.
 10. The method of claim 9, wherein the step ofmodifying comprises: generating one or more non-linear components of thesecond digital signal based, at least in part, on the determined one ormore non-linear coefficients; and subtracting the generated one or morenon-linear components from the second digital signal.
 11. The method ofclaim 9, further comprising: filtering the first and second digitalsignals; and selecting one of the filtered first digital signal and thefiltered second digital signal for further processing.
 12. The method ofclaim 11, wherein the step of selecting comprises: selecting thefiltered first digital signal when a signal strength associated with aninput signal used to generate the first digital signal is equal to orexceeds a threshold signal strength; and selecting the filtered seconddigital signal when the signal strength associated with the input signalused to generate the second digital signal is less than the thresholdsignal strength.
 13. An apparatus, comprising: a controller configuredto perform steps comprising: receive a first digital signal from a firstanalog to digital converter (ADC); receive a second digital signal froma second ADC, wherein the second digital signal is more non-linear thanthe first digital signal; determine one or more non-linear coefficientsof the second digital signal based, at least in part, on processing ofthe first and second digital signals; and modify the second digitalsignal based, at least in part, on the determined one or more non-linearcoefficients to generate a more linear second digital signal.
 14. Theapparatus of claim 13, wherein modifying, by the controller, comprisesthe controller being further configured to perform the steps comprising:generating one or more non-linear components of the second digitalsignal based, at least in part, on the determined one or more non-linearcoefficients; and subtracting the generated one or more non-linearcomponents from the second digital signal.
 15. The apparatus of claim13, wherein the first ADC comprises a closed-loop ADC.
 16. The apparatusof claim 13, wherein the second ADC comprises an open-loop voltagecontrolled oscillator-based (VCO-based) ADC.
 17. The apparatus of claim13, wherein the controller is further configured to perform stepscomprising: filtering the first and second digital signals; andselecting one of the filtered first digital signal and the filteredsecond digital signal for further processing.
 18. The apparatus of claim17, wherein selecting, by the controller, comprises the controller beingfurther configured to perform steps comprising: selecting the filteredfirst digital signal when a signal strength associated with an inputsignal used to generate the first digital signal is equal to or exceedsa threshold signal strength; and selecting the filtered second digitalsignal when the signal strength associated with the input signal used togenerate the second digital signal is less than the threshold signalstrength.
 19. The apparatus of claim 13, wherein the controllercomprises an audio coder/decoder (CODEC).